We test a D $=0\mathrm{.}6$ m diameter rotor with B $=16$ blades. Assume the speed of sound to be a

$=340$ m$/$s$.$

$1.$ When the rotational tip Mach number becomes sonic, what is the revolution per minute

$($RPM$)$ of the rotor speed?

$2.$ What is the blade passing frequency $($BPF$)$ at this RPM$?$

$3.$ We tested this rotor as an open rotor at this RPM and measured sound pressure level

$($SPL$)$ of BPF at $90$o microphone as $100$ dB$.$ If we were to take out half of the blades and

run at the same RPM$,$ what is the SPL at BPF$?$ Assume that each blade carries the same

loading regardless of the number of blades.

$4.$ If we keep $16$ blades but reduce the RPM by $20\%$ and assume that the incompressible

Bernoulli equation is valid $($i$.$e$.$ p ~

$$u$2/2,$ T & Q ~ u$2),$ what is the SPL at BPF$?$